That's a good question: I have a lot of references to his revolvers, but no specific information on carbines or rifles. He did have, and was interned with a U.S. Springfield 50-70 that had been sporterized, but this would be post-war.
At the beginning of the war he worked as a freighter, driving a wagon – and later became a scout. It is possible that he depended on his brace of revolvers and didn’t carry a long-gun, for the same reason that Pony Express riders didn’t – to save weight. Joseph G. Rosa might know, and maybe he could be reached in the U.K., but I don’t have a current address.